I have the same problem, from time to time music skips ahead a second or two.
This happens usually once or twice in every track, mp3 or flac doesn’t matter.
It is very annoying, I would love to get to the bottom of this.
I’m running the server on Ubuntu, the problem has been there for the latest many versions (1.6, 1.8, 1.11, 1.12, 1.13 and 1.15), and all all players.
I never had this issue before, but now I am at a job site with crappier WiFi/internet bandwidth than my main office. I was able to play two albums before noticing this issue. Then on the 3rd album, songs started stuttering. Bitrate for FLAC files between the albums isn’t too different, all around 900kbps.
Playing in Plex Web in Chrome does not stutter, but also transcodes to AAC.
I suspect this is a bandwidth limitation, perhaps exacerbated by a bug. It seems that my bandwidth should be enough to cover it.
Plex server: 1.16.2.1297
Plex Web: 3.99.2
Plex Amp: 1.1.0